IO-Link™ is a standardized IO technology for point-to-point communication with sensors and with actuators using a system realized as shown in FIG. 1. Sensors and/or actuators of the system are each connected to a respective port of a slave device, that collects data and transmits them to a master device through a cable. On its turn, the master device is connected to a PLC (Programmable Logic Controller) that controls the whole system through a bus.
The ports of the IO-Link™ devices may be of the type shown in FIG. 2. A master device is connected to a slave device as shown in FIG. 3, through a three-wire cable that includes a positive supply line L+, a negative supply line L− and a digital data line C/Q. The master device thus provides power supply to the slave device and communicates thereto through the digital data line, on which a switching data signal is transmitted.
FIG. 4 shows a typical scheme of a slave IO-Link™ device, that may optionally include a microcontroller, eventually coupled to a sensor or actuator, and an IO-Link™ transceiver that interfaces the microcontroller with the three-wire cable. The transceiver sends to/receives from the microcontroller signals of information (RX, TX) of data to be sent through the data line C/Q of the cable, and provides to the microcontroller an internal supply voltage Vcc.
If the cable is connected to the pins of the transceiver with inverted polarity, the voltages on the power supply pins L+, L− and on the input/output pin C/Q may be such as to damage the microcontroller or even the inner circuits of the transceiver itself. For safety reasons of the internal components of the device, present transceivers for IO-Link™ applications include a protection circuit, typically comprising passive components such as Zener diodes or Schottky diodes. The Zener diodes ensure protection from overvoltage on the line, and the Schottky diodes prevent destructive current flow in case of a reverse polarity connection, i.e. when the power supply pins L+, L− are connected with inverted polarity to the respective supply lines of the cable. With this technique, potentially destructive voltages are prevented from being distributed internally to the IO-Link™ device.
FIG. 5 depicts a transceiver E981.10 manufactured by Elmos coupled to a microcontroller. The protection circuit is provided by the external TVS (Transient-Voltage-Suppression) diodes between the data line C/Q and ground, by the diode between the data line C/Q and the positive supply line L+ and by the diode in series to the positive supply line L+. Such a protection circuit is relatively expensive because it uses external passive components; moreover, the diode connected in series to the positive supply line increases power losses.
FIG. 6a illustrates how to connect the transceiver MAX14820 manufactured by Maxim, and FIG. 6b shows the internal architecture thereof. This known transceiver has a protection circuit including external diodes (FIG. 6a) connected between the data terminals C/Q, DO and the auxiliary supply voltage input VP, and of the two internal diodes highlighted in FIG. 6b. Also for this transceiver, external passive components are required.
Another transceiver for IO-Link applications, manufactured by HMT Microelectronic AG, is depicted in FIG. 7. The protection circuit is includes passive components, namely two diodes and two Zener diodes, that occupy a relatively large silicon area and, in general, reduce power efficiency of the system.